The fabrication sequence of integrated circuits often includes several patterning processes. The patterning processes may be used to define a layer of conducting features which may be formed in metal, polysilicon or doped silicon. Thereafter, electrically isolating structures may be formed by depositing dielectric material on the patterned layer which includes trenches located between electrically active regions. The dielectric material provides electrical isolation within the plane of deposition but also between vertically separated layers of conducting features.
A challenge associated with the formation of sub-micron devices is filling a narrow trench in a void-free manner. To fill a trench with silicon oxide, a layer of silicon oxide is first deposited on the patterned substrate. The silicon oxide layer typically covers the field, as well as walls and bottom of the trench. If the trench is wide and shallow, it is relatively easy to completely fill the trench. As the trench gets narrower and the aspect ratio (the ratio of the trench height to the trench width) increases, it becomes more likely that the opening of the trench will be closed (or “pinched off”) before the trench is completely filled.
Pinching off a trench may trap a void within the trench. Under certain conditions, the void will be filled during a reflow process, for example where the deposited silicon oxide is doped and experiences viscous flow at elevated temperatures. However, as the trench becomes narrower, even reflow processes may have difficulty filling the void. Moreover, several types of applications call for the deposition of lightly or undoped silicon oxide, which can be difficult to reflow even at an elevated temperature. Voids resulting from pinching-off are undesirable as they can reduce the performance and yield of good chips per wafer as well as the reliability of the devices.
Flowing TEOS and Ozone (O3) to a processing chamber is a technique used to create a silicon oxide film which can fill high aspect ratio trenches well due to the high initial mobility on the substrate. Trenches can be filled without voids at relatively high substrate temperatures (above 600° C.). Additives may be used such as water vapor to further reduce the initial viscosity of the film thereby reducing or eliminating the need to reflow the film in a subsequent step. Using similar precursors at lower substrate temperatures results in spatially varying film growth rates. Film growth rate irregularities can act to trap voids within a trench thereby reducing the benefits of using a TEOS/Ozone process.
Therefore, it is desirable to be able to fill narrow trenches with silicon oxide films at lower temperatures without leaving voids.